剑指 Offer II 055. 二叉搜索树迭代器

解题思路

1.将二叉树转换为链表
2.内部维护currentindex与list，来获取next和判断是否已经遍历到尾端

解题遇到的问题

无

后续需要总结学习的知识点

源码的遍历如何实现的？

##解法1
import java.util.ArrayList;
import java.util.List;

class BSTIterator {
    List<Integer> listvalue = null;
    int currentIndex = 0;

    public BSTIterator(TreeNode root) {
        listvalue = new ArrayList<>();
        addList(root);
        currentIndex = 0;
    }

    public int next() {
        return listvalue.get(currentIndex++);
    }

    public void addList(TreeNode node) {
        if (node == null) {
            return;
        }

        addList(node.left);
        listvalue.add(node.val);
        addList(node.right);
    }

    public boolean hasNext() {
        return currentIndex < listvalue.size();
    }

    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode() {
        }

        TreeNode(int val) {
            this.val = val;
        }

        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }
}